Asphalt-based roofing materials, such as roofing shingles, roll roofing, and commercial roofing, have long been installed on the roofs of buildings to provide protection from the elements and to give the roof an aesthetically pleasing look. Typically, asphalt-based roofing material is constructed of a substrate such as a glass fiber mat or an organic felt mat, an asphalt coating on the substrate to provide a water barrier, and a surface layer of granules embedded in the asphalt coating. The granules protect the asphalt from deterioration due to exposure to UV and IR radiation from the sun and due to direct exposure to the elements.
A common method of manufacturing asphalt-based shingles is to advance a web of material through a coater, which coats the web with liquid asphalt forming a hot tacky asphalt coated substrate. The asphalt coated substrate typically is then passed beneath one or more granule dispensers, which discharge or dispense protective and decorative surface granules onto at least selected portions of the moving asphalt coated substrate. A granule dispenser may be as simple as a direct feed nozzle fed by an open hopper that is filled with granules or as complex as a granule blender. The result is an elongated substrate of shingle stock, which can later be sliced and cut to size to form individual shingles, cut and rolled to form a rolled shingle, or otherwise processed into final products.
In some shingle manufacturing processes, there is a need to deliver granules at intermittently timed intervals such that granules are deposited on the asphalt coated substrate in spaced generally rectangular patches. In such cases, several mechanisms have been used in the past to start and stop the delivery of granules in a controlled manner to drop granules intermittently. For example, a fluted roll and gate assembly has been installed at the bottom of a granule dispenser nozzle. Rotation of the fluted roll through a predetermined angle pulls a charge of granules from a granule hopper and drops the granules a set distance (generally 12 inches or more) onto the asphalt coated substrate below. In some cases, the charge of granules slides down a polished curved surface toward the substrate material. The curved surface in conjunction with gravity may accelerate the charge of granules to approximately the speed of or slightly greater than the speed of the moving asphalt coated substrate below. In this way, the charge of granules is deposited more gently onto the asphalt, to which the granules stick to form the protective decorative coating.
Prior systems and methods for depositing granules onto an asphalt coated substrate in shingle manufacturing have exhibited a variety of inherent problems. Chief among these is that as the speed of production increases, meaning that the speed of the moving asphalt coated substrate increases, the edges and patterns of dispensed charges of granules on the asphalt become less and less defined. Eventually, the deposited patterns of granules are so indistinct and distorted as to be unacceptable in appearance, coverage, and protection. Trailing edges in particular of a deposited charge of granules become more and more smeared out as the speed of production is increased and dispensed charges of granules exhibit unacceptable trailing patterns. As a result, granule delivery systems and methods in the past have been practically limited to production speeds below about 800 feet per minute (fpm) of asphalt coated substrate travel, also referred to as machine speed or line speed. This can be a bottle neck since other areas of production such as asphalt application are capable of moving much faster.
Modern asphalt roofing shingles may have granules of several colors arranged in spaced patches to provide a pleasing aesthetic and the appearance of texture when the shingles are installed. A common example is patches of three colors; a blend or background color, a dark color, and a light color. These patches may be arranged in any of a number of sequences such as, for instance, blend-dark-blend-light-blend-dark-blend-light and so on. When manufacturing such shingles, it is necessary that the lines of demarcation between the different color patches be sharp and well defined. Otherwise, the shingles will not have a commercially acceptable appearance. However, at higher line speeds above about 800 FPM, it becomes difficult with traditional granule application techniques to maintain well defined lines of demarcation because, among other things, of the indistinct trailing edges of granule drops mentioned above.
There is a need for a granule delivery system and method for use in shingle manufacturing that is capable of delivering a charge of granules at intermittently timed intervals onto a moving asphalt coated substrate with precision, definition, and controllability and at manufacturing or line speeds of over 800 FPM and even over 1000 FPM. There is a further need for a method of depositing patches of different color granules with well defined lines of demarcation between adjacent patches at high line speeds. It is to the provision of such an apparatus and method that the present invention is primarily directed.